Vacuum packaging in heat sealable plastic bags is a conventional way of packaging food items such as whole fowl, cuts of meat, cheese bricks and the like for sale at retail. Vacuum packaging involves placing the food item in a heat sealable plastic bag and then communicating the bag to a partial vacuum to evacuate air from the bag and collapse it about the food item. The bag is heat sealed in its evacuated condition so the food item becomes encased in a generally air-free environment.
It also is customary to fabricate the bag from a heat shrinkable plastic film. After sealing, the bagged food item is immersed in hot water or otherwise exposed to heat to shrink the bag so it is tight about the food item. This makes the bag substantially wrinkle-free and enhances the appearance of the bagged article for retail sale.
Apparatus, as disclosed for example in U.S. Pat. No. 3,958,391, has been developed to automate the vacuum packaging operation. The apparatus as disclosed in this patent has a plurality of platens arranged for movement along a closed path of travel. Each platen includes a heat sealer and is adapted to receive a bagged article wherein the open mouth of the bag is draped across the heat sealer.
During the course of moving through its closed path of travel, each platen merges with a vacuum chamber. The chamber presses against the platen and, for a portion of the path, it moves along with the platen. During this time the chambers are evacuated to remove air from the bags and the heat sealers are operated to close the bags. Each vacuum chamber then vents to atmosphere and thereafter separates from the platen so the bagged article can be removed.
Since each platen has its own heat sealer, provision must be made for supplying electrical power to each platen moving along the path of travel. It also is customary to supply each platen with other utilities. For example, water is supplied for cooling the heat sealer and pressurized air is supplied for closing the heat sealer. The need for multiple heat sealers and for supplying several utilities to each platen compounds maintenance problems and the systems required to supply multiple utilities to each moving platen adds to the complexity of the system.
The present invention eliminates the need for multiple heat sealers and for the delivery of electrical power, cooling water and other utilities to each platen moving through a closed path of travel. Instead, each platen in the present invention is provided with a mechanically operated clamp. The clamp closes about the bag after evacuation and maintains the bag in an evacuated state even after the vacuum chamber separates from the platen. The path of travel followed by each platen carries it to a heat sealing zone containing at least one operable heat sealer which operates to heat seal each bag carried by a platen through the heat sealing zone.